The present invention relates to the determination of the profile of a bed of a furnace, such as the smelt bed of a boiler. Secondarily, the present invention relates to displaying information concerning the bed profile and to utilizing this information in the control of the furnace.
The monitoring of a hot infrared emitting surface or bed obscured by particulate fume and hot gases, such as found in Kraft pulp recovery boilers is a difficult task. That is, interference from fume particles and gaseous radiation within the furnace tends to obscure the view of hot surfaces, such as of the smelt bed, under such adverse environmental conditions.
U.S. Pat. No. 4,539,588 to Ariessohn, et al. describes one form of an apparatus for this purpose. In particular, the Ariessohn, et al. device comprises a closed circuit video camera fitted with an infrared imaging detector or vidicon tube. An objective lens obtains the image. An optical filter interposed between the lens and vidicon is selected to reject radiation in all but limited ranges of radiation to avoid interference by gaseous species overlaying the smelt bed, such gases being strongly emitting and absorbing. As a specific example, a spectral filter centered at 1.65 micrometers with a band width of 0.3 micrometers is suitable for imaging a Kraft recovery smelt bed.
A product known as TIPS .TM. from the Sensor and Simulator Products division of Weyerhaeuser Company of Tacoma, Wash. incorporates the device of the Ariessohn, et al. patent in a temperature image processing and storage system. The TIPS system creates digitally colorized images of the smelt bed for use by an operator. In the TIPS system, due to the partial elimination of the affects of moving particles in the image, the view of active scenes on the bed is permitted. The TIPS system is especially designed for displaying temperature trends of the bed on digital and graphic displays and for tracking changes from a reference temperature at a selective location in the process, or to observe temperature differences between locations. In addition, the TIPS system allows the production and storage of historical temperature changes. Moreover, the TIPS system permits the manual adjustment of a reference temperature for purposes of comparison.
The capabilities of the TIPS system are described in greater detail in an article published in April of 1989 entitled "Monitoring of Recovery Boiler Interiors Using Imaging Technology," by Anderson, et al (CPPA-TAPPI 1989 International Chemical Recovery Conference). In addition to discussing the imaging of a bed for purposes of developing temperature trend information, this particular article mentions that adequate smelt reduction requires sufficient bed residence time, which is influenced by bed configuration. The article also recites that both of these issues can be addressed by a bed level monitoring system which can extract the bed profile and alert the operator when the bed drifts out of the user-defined range. The article then mentions that the Weyerhaeuser (TIPS) system has the capability to detect bed heights so as to provide a control signal for those interested in using bed height or slope for control purposes. However, this article does not provide any information on how these goals would be accomplished.
U.S. Pat. No. 4,737,844 to Kohola, et al. describes a system utilizing a video camera for obtaining a video signal which is digitized and filtered temporally and spatially. The digitized video signal is divided into signal subareas with feature elements belonging to the same subarea being combined into continuous image areas corresponding to a certain signal level. The combined subareas are then processed to provide an integrated image which is averaged to eliminate the effect of random disturbances. The averaged image is displayed on a display device. The images may then be compared to optimum conditions. Areas corresponding to effective combustion and the flame front of a bed, are then defined using histograms, and identified by means of their area, point of gravity coordinates of the area and point-by-point recorded contours of the area. In addition, the contours of voids inside the area are defined. In an application described in the Kohola, et al. patent, the flame front, location and shape of the fuel bed is determined.
In Kohola, et al., the material to be burned is shown as a bed of a substantially identical thickness and width. This bed is delivered to the mill end of a boiler stoker where the flame front is concentrated. Thus, Kohola, et al. is described in conjunction with a bed of a substantially uniform contour and is not directed toward beds such as are found in smelt bed boilers which are burning throughout substantially their entire surface and wherein the contours of the bed vary depending upon furnace operating parameters, such as the fuel to air ratio.
Although systems exist for monitoring the interior of recovery boilers and other furnaces, a need exists for an improved system for determining the profile of the bed, such as of a smelt bed, in the interior of such furnaces. The determined profile may then be displayed or optionally used, for example, in the control of the operation of the furnace.